D--048966 - CALFED Bay-Delta Program - State of California

and the City of Los Angeles. Smaller alluvial valleys include
Hydrology and Water Resources
tables in western Tuolumne County (comments by Tuolumne
Indian and American Valleys of the Feather River Basin, Tahoe Utility District in DEIS on Yosemite Estates). Ground-water
Valley in the upper Truckee River Basin, Slinkard and Bridge- pumping can also impact local stream flow. Interactions beport
Valleys of the Walker River Basin, and Long Valley in tween ground water and streams are very complex in some
the Owens River Basin. areas of the Sierra Nevada where glacial till is interlayered
Many wells in the Sierra Nevada are located in shallow with volcanic mudflows and ash and is dissected by old
deposits of glacial till, alluvium, and colluvium. These surficial stream courses and faults (Kondolf and Vorster 1992). Drilldeposits,
which are often only a few tens of meters deep (Page ing of supplemental water-supply wells for Mammoth Lakes
et al. 1984; Akers 1986), are fairly porous and convey water to raised concerns that pumping could further reduce flows in
streams. Deeper deposits are capable of serving the needs of Mammoth Creek, which is already diverted as the principal
small communities but may be sensitive to recharge condi- water source for the town (Kattelmann and Dawson 1994).
tions. Placer County (1994) has determined that ground wa- In a small lake basin in the alpine zone of Sequoia National
ter in the foothills is not a reliable source of water for future Park, water released from short-term subsurface storage acgrowth,
counted for less than 15% of the annual stream-flow volume,
Some rocks and other geologic formations, like buried river but it controlled the chemistry of stream and lake water for
channels, are relatively porous and transmissive. Hydro- more than two-thirds of the year (Kattelmann 1989b).
geologic properties of these formations are highly variable, Springs are an important water source for small demands
as are well yields. Locating a well is often hit-or-miss, but that require minimal development. Because springs are often
drillers familiar with an area can usually find sources of wa- fed by shallow aquifers, they are more susceptible to contamiter
adequate for residential use. Mixed results have been ob- nation than deep sources and often require protection of their
tained in recent drilling through the complex layers of till, contributing areas. Dense vegetation resulting from decades
volcanic ash, and basalt found in the Mammoth Lakes area. of fire suppression may maximize transpiration losses from
Some wells have been highly productive, and others have hill slopes above springs, thereby reducing spring flow. Dequickly
gone dry. veloping springs as a water source usually alters or even elimi-
Granitic and metamorphic rocks of the Sierra Nevada are nates riparian and aquatic habitat in the immediate area.
essentially impermeable except where fractured. In some Io- Springs are one of the most threatened habitats in the Sierra
cations, the joint and fracture systems can transmit signifi- Nevada (see Erman 1996). Springs as well as pumped water
cant quantities of water. A recent study in the Wawona area are commercially developed for packaging as mineral water.
of Yosemite National Park investigated fracture systems and Bottled water operations are present in the northern and
the regional movement of deep ground water (Borchers et al. southern Owens Valley.
1993). Most wells in southwestern Nevada County, and presumably
in other parts of the foothills with similar geology, Ground-Water Quality
are located in areas of fractured rock (Page et al. 1984). Of
some 13,000 wells drilled in Placer, E1 Dorado, Amador, and The mineral content of ground water is generally much higher
Calaveras Counties between 1960 and 1982, more than 90% than that of surface water. The long residence time of water
were located in hard rock (California Department of Water in the ground allows it to dissolve minerals and accumulate
Resources 1983). The size and frequency of fractures decline ions. Nevertheless, total dissolved solids in ground water in
with depth away from the surface, so the more productive the Sierra Nevada are usually not an impediment for use.
wells in Nevada County have been less than 60 m (200 ft) Deeper ground water in parts of the Honey Lake/Long Valdeep.
Mean yield in that study area was less than 70 1/min ley Basin and the Mono basin and below Mammoth Lakes
(18 gal/min) (Page et al. 1984), with about half the wells yield- contain substantial concentrations of various ions. Concening
less than 38 I/min (10 gal/min) (California Department trations of naturally occurring iron are sometimes too high
of Water Resources 1974). Average well yields determined for domestic uses (Thornton 1992; Placer County 1994). Some
from drillers’ logs were less than 80 I/min (20 gal/min) in wells in Kern Valley have very high levels of fluoride. Shalboth
Nevada and Amador Counties (Harland Bartholomew low ground water may be contaminated with nutrients from
and Associates et al. 1992; California Department of Water septic and sewage disposal systems, livestock, and chemicals
Resources 1990a). Wells in Tuolumne County are often more applied to farms and gardens. Nutrients found in ground
than 90 m (300 ft) deep and are adequate for domestic use. water in the Lake Tahoe Basin were relatively low in an abso-
The drought between 1987 and 1992 limited recharge through- lute sense, but they still contributed to enrichment of the lake
out the Sierra Nevada, and yields of many wells declined waters (Loeb and Goldman 1979). Water quality problems of
through the period. There is insufficient information avail- the larger ground-water basins in the Sierra Nevada identiable
to determine whether the proliferation of wells through- fled in the biennial state water quality assessment included
out the foothills in the past decade has had a pronounced effect drinking water impairment from heavy metals, fuel leaks,
on preexisting wells, volatile organic compounds, naturally occurring radioactiv-
Pumping of water for industrial uses has lowered water ity, pesticides, and wastewater (California State Water Re-
D--048993
D-048993